Question

Determine the amount of energy needed to melt a 5.0 kg block of lead if it is heated from a temperature of 23.0 degrees Celsius. The melting point of lead is 327.5 degrees Celsius.

Answer 1

Given,

Mass of lead,  
m 5kg

Initial temperature, $T_i=23\degree C$

Final Temperature,
Tf 327.5°C

We know that specific heat of lead is $130Jkg^{-1}K^{-1}$ and latent heat of fusion of lead is .

When we start heating the block, two thing will happen:-

1) The temperature will increase from initial to final temperature.

2) State of lead will change from solid to liquid.

Heat reqquired to change the temperature from $T_i$ to $T_f$ is,

$Q_1 = ms\Delta T$

Heat required to change the state of lead from solid to liquid is,

$Q_2=m*l$

$Q_2=5*23000$

$Q_2=115000J$

Total heat required, $Q=Q_1+Q_2$

$Q=(197925+115000)J$

$Q=312925J$

$Q=3.13*10^{5}J$